Date Published: March 25, 2019
Publisher: Public Library of Science
Author(s): Seiji Hamanishi, Eri Eguchi, Tatsuo Ito, Kenjiro Nagaoka, Keiki Ogino, Thomas Penzel.
Although selective head-cooling has been reported to decrease scalp and tympanic temperature and improve sleep quality, whether head-cooling during sleep can improve sleep quality in women during the luteal phase has not been elucidated. This randomized, controlled crossover open trial aimed to investigate the effect of head cooling during sleep on sleep quality in women during the luteal phase. Female university students aged 19–25 years with increased daytime sleepiness during the luteal phase were recruited by poster advertisement at their university from May to June 2016 and from May to June 2017. Fourteen women aged 19–22 years participated in this study. The temperature-controllable cooling sheet containing tubes filled with circulating water was used for head-cooling, and the head-cooling and the controlled temperature were set at 25°C and 35°C, respectively. Electroencephalogram data were obtained using a single-channel portable electroencephalogram device. The difference in sleep-related variables and tympanic temperature between head-cooling and control were analyzed using a linear mixed model. The proportion of arousal was lower with head cooling than with the control. In contrast, the proportion of non-REM3 and the delta power were higher with head cooling than with the control. The proportion of non-REM2 and non-REM3 among sleep EEG stages were positively and negatively correlated with the mean tympanic temperature during sleep, respectively. However, arousal and REM were not correlated with tympanic temperature. We considered the reduction of arousal time by head-cooling might be related to scalp temperature rather than tympanic temperature. Further, our results suggested that head-cooling also improved subjective sleep comfort. In conclusion, head-cooling during sleep could improve sleep quality in young women during the luteal phase.
The menstrual cycle is regulated by ovarian hormones including estrogen and progesterone, and many women repeatedly experience physical and psychological changes during menstruation or the luteal phase [1, 2]. Premenstrual syndrome (PMS) refers to the behavioral or social dysfunction due to physical or psychological symptoms during the luteal phase [1, 2]. In particular, the severe psychiatric symptoms of premenstrual dysphoric disorder (PMDD), a severe form of PMS, could impair the social life and human relations of reproductive-age women [3–5]. The sleep-related problem is one of the major premenstrual symptoms. Premenstrual hypersomnia and daytime sleepiness in reproductive-age women have been reported, with their prevalence being higher in patients with PMS or PMDD . Premenstrual hypersomnia and sleepiness are most likely influenced by poor sleep quality [6, 7]. It is suggested that, among the sleep stages determined using electroencephalogram (EEG), rapid eye movement (REM) decreases, whereas arousal and non-REM stage 2 increase in the luteal phase [8–12]. Moreover, previous studies reported that subjective sleep quality deteriorates in the late luteal phase [6, 12, 13]. Changes in sleep quality during the luteal phase may be affected by an increase in body temperature due to increased progesterone . As progesterone inhibits heat loss, the core body temperature increases by 0.3–0.5°C and the temperature rhythm amplitude decreases in the luteal phase . Consequently, the core body temperature remains high during sleep [13–15]. Sleep quality is affected by the core body temperature, with sleep being inhibited unless the body temperature sufficiently decreases [16–18]. Several studies reported that selective head-cooling could decrease scalp and tympanic temperature and improve sleep quality [19–21]. However, to our knowledge, whether head-cooling during sleep can improve sleep quality in women during the luteal phase has not been elucidated. This study aimed to elucidate whether head cooling during sleep can improve sleep quality in women during the luteal phase.
To our knowledge, the present study is the first to report that head-cooling during sleep can improve sleep quality during the luteal phase in healthy young women with daytime sleepiness or premenstrual hypersomnia. Further, enhancing sleep quality using head-cooling may contribute to improvement in the quality of life in reproductive-age women with daytime sleepiness during the luteal phase.
Our study showed that head-cooling during sleep decreased the tympanic temperature and improved the part of sleep-related variables including sleep EEG. Our results may support the future study to examine whether head-cooling during sleep may be an effective strategy to improve sleep quality in the luteal phase in reproductive women.